1. Field
The present invention relates to a method of manufacturing a semiconductor package and to a semiconductor plastic package manufactured using this method.
2. Description of the Related Art
Current electronic devices are trending towards smaller, thinner, and lighter products. In step with these trends, the preferred methods for mounting semiconductor chips are changing from wire bonding methods to flip chip methods, which allow greater numbers of terminals. Furthermore, there is a demand also for higher reliability and higher densities in the multilayer printed circuit board, to which semiconductor chips may be mounted.
In the conventional multilayer printed circuit board, if fiberglass woven fabric is used for the base material, E-glass is generally used for the glass component.
A thermosetting resin composition may be impregnated into the fiberglass woven fabric, dried, and put in a B-stage condition, which can then be processed into a copper clad laminate. This copper clad laminate can be used to fabricate a printed circuit board core, for use in the inner layers, after which B-stage insulation sheets may be arranged and stacked as build-up layers, to manufacture a multilayer printed circuit board.
In the multilayer printed circuit board thus manufactured, a build-up resin composition may be used in many of the layers, which has a high rate of thermal expansion (generally about 18 to 100 ppm/° C. in the longitudinal and lateral directions), and a copper (Cu) layer having a rate of thermal expansion of about 17 ppm/° C. may be included in each layer. On the outermost layers, solder resist layers may be formed which also have a high rate of thermal expansion (generally about 50 to 150 ppm/° C.). Consequently, the overall coefficient of thermal expansion in the longitudinal and lateral directions for the multilayer printed circuit board may be about 10 to 30 ppm/° C.
If an aromatic polyaramid fabric is used as a reinforcing material, the rate of thermal expansion in the longitudinal and lateral directions of a double-sided printed circuit board used for the inner core can become 10 ppm/° C. or lower. Even so, if additional build-up resin compositions and copper layers are included with this board to manufacture a printed circuit board having a large number of layers, the rate of thermal expansion may be increased to a value over 10 ppm/° C.
However, due to the difference in thermal expansion between the semiconductor chip and the multilayer printed circuit board, the many-layered printed circuit board manufactured using an aromatic polyaramid fabric can have lower strength compared to a printed circuit board manufactured using fiberglass non-woven fabric over the entire printed circuit board, so that bending and warpage are more likely to occur. Also, since the reinforcing material and resin are organic substances, the rate of thermal expansion may be greater in the thickness direction in the multilayer printed circuit board, which can lead to problems in reliability.
Even in cases where E-glass fiber woven fabric and aromatic polyaramid fabric are used together, the effect of the resin for the build-up layers as well as of the copper layers, which may have a rate of thermal expansion of about 17 ppm/° C., may make it difficult to manufacture a printed circuit board having a rate of thermal expansion of 10 ppm/° C. in the longitudinal and lateral directions, let alone 9 ppm/° C. or lower.
When mounting a semiconductor chip to this type of multilayer printed circuit board, an underfill resin may be used to provide a structure that absorbs the stresses caused by expansion or contraction when the board is heated or cooled. However, in cases where a semiconductor chip is mounted and connected that has a rate of thermal expansion of 2 to 3 ppm/° C., the difference in thermal expansion can cause bending or warpage. When reliability tests are performed, including temperature cycle tests, etc., for a semiconductor chip mounted and connected without using an underfill resin, especially a semiconductor chip having a rate of thermal expansion of about 3 ppm/° C. connected using lead-free solder, etc., defects may occur, such as cracking in the lead-free solder and semiconductor chip, and detaching between the semiconductor chip and the solder, etc.
Consider the case of a multilayer printed circuit board that uses carbon fiber woven fabric and a metal plate made of copper-Invar, etc., in the center as a core, and includes insulation layers coated over the core. For this multilayer printed circuit board also, the effects of the resin for the build-up layers as well as of the copper layers, which may have a rate of thermal expansion of about 17 ppm/° C., may result in a rate of thermal expansion of 10 ppm/° C. or higher. Moreover, this type of multilayer printed circuit board may entail high material costs, difficult processing procedures, and other problems in terms of reliability and economy. Also, using an underfill resin may not be cost-effective, since it may prevent rework in the package in the event of a malfunction in the semiconductor chip or multilayer printed circuit board, and thereby render the entire semiconductor plastic package defective.